Display screen or portion thereof with transitional graphical user interface



FIG. 1 is a front view showing a first image in a sequence for a display screen or portion thereof with transitional graphical user interface showing our new design;

FIG. 2 is a front view showing a second image thereof; and,

FIG. 3 is a front view showing a third image thereof.

The appearance of the transitional graphical user interface sequentially transitions between the images shown in FIGS. 1-3. The process or period in which one image transitions to another forms no part of the claimed design. The broken lines within the figures show unclaimed portions of the transitional graphical user interface, and the broken lines around the figures showing of the display screen are included for the purpose of illustrating environment structure; the broken lines form no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with transitional graphical user interface, as shown and described. 